Didn't disable Aero, but did the following (and noticed a slight improvement)
Turned graphics down from 'Ultra' to 'High' on the main wow
Set my system to High Performance in power mgmt, tweaked everything so CPU/vid etc all runs at 100% capacity

Then I stumbled upon the ultimate performance boost yesterday while playing. Boosted me from ~20fps to ~60fps:

Login to my L80 main in Orgrimmar, visit the AH, then log back into the 'lead' toon of the multibox team. Presto, now they've got 60fps as well ?!?